Gas detecting and measuring device

ABSTRACT

A DEVICE FOR THE DETECTION OF AND QUANTITATIVE MEASUREMENT OF A GAS IN A GIVEN ENVIRONMENT, SUCH AS ALCOHOL IN THE BREATH OR CARBON MONOXIDE IN THE ATMOSPHERE, IS DESCRIBED. THE DEVICE COMPRISES INTAKE AND FLOW CONTROL MEANS FOR THE GAS SAMPLE, AND AN ELECTROCHEMICAL CELL HAVING AN ANODE WHICH PROVIDES A SITE FOR ELECTROCHEMICAL REACTION OF THE GAS BEING DETECTED, A CATHODE, A REFERENCE ELECTRODE, AND AN ELECTROLYTE IN CONTACT WITH THE ANODE, CATHODE, AND REFERENCE ELECTRODE. THE ANODE, TO ENSURE THAT THE CURRENT PRODUCTION IS A RESULT OF THE GAS BEING DETECTED AND NOT OTHER GASES, INTRODUCING OXYGEN, IS MAINTAINED AT A FIXED POTENTIAL IN RELATION TO THE POTENTIAL OF THE REFERENCE ELECTRODE. THE DEVICE PROVIDES AN ACCURATE AND INEXPENSIVE MEANS OF DETECTING AND QUANTITATIVELY MEASURING A GAS CONTAINED IN A GIVEN ENVIRONMENT, I.E., ALCOHOL IN THE BREATH OF THE SUBJECT BEING TESTED OR CARBON MONOXIDE IN THE ATMOSPHERE.

July 16, 1974 H. G. OSWIN ETAL 3,324,167

GAS DETECTING AND MEASURING DEVICE Filed Aug. 17, 1971 3 Shaets-$haet lF/Gj Q n lA/VE/VTO/ZS,

Jul 16, 1974 H. G. OSWIN ETAL GAS DETECTING AND MEASURING DEVICE 3Sheets-Sheet 2 Filed Aug. 17, 1971 Jufiylfi, 1974 H. G. swlN ETAL3,324,167

GAS DETECTING AND mmsunme'nnvzcn Filed Aug. 1'7, 1971 3-sheets -shnet 3United States Patent 01 fice 3,824,167 Patented July 16, 1974 PublicInt. 'Cl. G01n 27/46 U.S. Cl. 204-195 R 16 Claims ABSTRACT OF THEDISCLOSURE A device for the detection of and quantitative measurement ofa gas in a given environment, such as alcohol in the breath or carbonmonoxide in the atmosphere, is described. The device comprises intakeand flow control means for the gas sample, and an electrochemical cellhaving an anode which provides a site for electrochemical reaction ofthe gas being detected, a cathode, a reference electrode, and anelectrolyte in contact with the anode, cathode, and reference electrode.The anode, to ensure that the current production is a result of the gasbeing detected and not other gases, including oxygen, is maintained at afixed potential in relation to the potential of the reference electrode.The device provides an accurate and inexpensive means of detecting andquantitatively measuring a gas contained in a given environment, i.e.,alcohol in the breath of the subject being tested or carbon monoxide inthe atmosphere.

This application is a continuation-in-part of our copending applicationU.S. Ser. No. 88,267 filed Nov. 10,

1970, now U.S. Pat. No. 3,776,832.

FIELD OF INVENTION AND BACKGROUND This invention relates to a device fordetecting and quantitatively measuring the quantity of a select gas in agaseous medium. More particularly, the invention relates to a devicewhich is compact, dependable, easy to operate, and relativelyinexpensive for detecting and quantitatively measuring a gas such ascarbon monoxide, hydrocarbons or an alcohol in an environment. Thedevice includes intake means, means for pumping the gas being analyzed,and an electrochemical cell for detecting and quantitatively measuring aselect gas. Although the invention is not limited thereto, forconvenience it will be described with reference to a device fordetecting and measuring the alcoholic content in the breath of a testsubject or for detecting and measuring carbon monoxide in a givenenvironment. As will be apparent, however, the device can be modified oradapted for detecting and measuring hydrocarbons including separation ofsaturated and unsaturated hydrocarbons, gases capable of being convertedto alcohols, carbon monoxide, or hydrocarbons, or other gases which canbe electro-chemically consumed, where similar conditions apply.

Alcohol Detection Although the social problem of the drinking or drunkendriver is not new, the ever-increasing number of cars on the highway andthe increasing horsepower and speed of these cars is greatly enhancingthe problem of the drinking or drunken driver. As a result, in the pastfew years insurance companies and safety groups have been publicizingthis social deficiency, emphasizing the uncontestable fact that alcoholconsumption on the part of drivers lead to impaired driving attitudesand habits. After the consumption of alcoholic beverages, both judgmentand reaction times deteriorate, resulting in a greater probability thatthe driver will be involved in a car accident.

Because of the greater public awareness of the drunken or drinkingdriver, some states have adopted legislation aimed at the drunkendriver, sometimes referred to as driving while drinking laws, and otherstates are considering such laws. These laws, to be enforceable, mustset objective standards as to what constitutes intoxication. Moreover,for the laws to be effective, the level of intoxication of any drivermust be easily and reproducibly established-preferably at roadside-by amethod which is socially acceptable, i.e., not offensive to the publicas a result of the manner in which the test is conducted.

To date, the blood alcohol level is the only quantitative measurementknown for determining intoxication which can be made with sufficientaccuracy and which is independent of physiological and psychlogicalvariations from one individual to the next. Although direct quantitativetests on the Whole blood are the most accurate, such tests areunsatisfactory in view of the need to take a blood sample from the testsubject and the relatively complex analytical tests required. todetermine alcohol levels of whole blood. Although the alcohol content ofurine can be correlated to the alcohol content of blood in the testsubject, it is not easy to obtain a urine sample for analysis, at leastnot at roadside; and, moreover, the correlation of the alcohol contentin urine with the alcohol content of blood requires a relatively complexanalysis. Additionally, a time factor is involved in the alcoholreaching the urine after consumption of the alcohol. Therefore, mosttests being considered by law enforcement and other concerned agenciesare based on the alcoholic content of the test subjects breath. It isfully established that not only is. alcoholic intoxication directlyrelated to blood alcohol level, but also that the blood alcohol leveland degree of a persons intoxication can be determined by the alcoholcontent of the test subjects breath derived from the alveolae. Thealveolae are the small bulbs in the lung wherein oxidation of bloodimpurities take place.

Although breath tests are socially acceptable, to be fully satisfactoryfor use by law enforcement personnel. the breath test method employedmust be (1) sufiiciently accurate an reliable to ensure that a highpercentage of drivers above the allowable limit and only a lowpercentage of those below the allowable limit will be detected andsubsequently charged with drunken driving;

(2) conducted in a hygienic manner with due regard to the health anddignity of the individual driver tested;

(3) conducted with portable and easy-to-operate equipment at roadside bya law enforcement officer of only average intelligence who has notechnical background or special training;

(4) rapidly carried out under all climatic conditions so that within afew minutes the apprehending oflicer can decide whether or not to chargethe test subject with drunken driving; and

(5) low-cost, including initial cost of equipment, maintenance andoperation of the equipment, and ofilcer training costs.

Although various methods have been suggested for determining the bloodalcohol level of a test subjects breath, none have met all of theaforesaid requirements. Most methods utilize chromatographic orcolorimetric determinations based on the oxidation of alcohol. Suchdevices having suflicient accuracy, however, are not suitable forroadside checks and/or are complex and/or are expensive precludingwidespread use. Moreover, presently available methods of collectingbreath samples, and methods of calibrating and verifying breath sampleshave various deficiencies.

Carbon Monoxide Detection The problems associated with carbon monoxidepollution and the need for carbon monoxide detectors, while being of asomewhat different nature for carbon monoxide detectors, while being ofa somewhat different nature than the problem associated with thedrinking driver and alcohol detection, are of no less social importance.As a result of increasing pollution, particularly in the major cities,with much of the pollution being the result of cars and other sourcesgiving off carbon monoxide, the need for a simple and rapid means ofdetermining and monitoring polluting gas levels in the atmosphere iscritical. Although various devices are available, including infra-reddetectors, chromagraphic or colorimetric devices, such units areexpensive and/or slow and difficult to use as a result of establishingor adjusting to a zero line, the need to remove any water present toavoid false readings, and the like. Moreover, such devices are onlymarginally portable.

OBJECTS AND GENERAL DESCRIPTION OF THE INVENTION Accordingly, a primaryobject of the present invention is to provide a compact, inexpensive,and easy-to-operate device for accurately and reproducibly detecting andquantitatively determining the level of a given gas in a specificenvironment.

Another object of this invention is to provide a compact, inexpensive,and easy-to-operate device for accurately and reproducibly detecting andquantitatively determining the blood alcohol level of a test subjectfrom a breath sample.

It is another object of this invention to provide improved methods ofcollecting breath samples from a test subject which do not permitcondensation of moisture in the breath and which permits the collectionof substantially only olveolar breath.

Another object of this invention is to provide a breath sample collectorhaving low energy surfaces with low heat transfer properties inhibitingthe condensation of water droplets thereby increasing the accuracy ofsubsequent tests on the sample.

It is another object of this invention to provide a calibrator for usewith blood alcohol level analyzers which is accurate, relativelyinexpensive, and easy to use.

It is another object of this invention to provide a breath sample from atest subject for confirmatory analysis at a later time.

It is another object of this invention to provide a device forelectrochemically detecting and quantitatively measuring the quantity ofcarbon monoxide in a gaseous medium.

It is another object of this invention to provide a device forelectrochemically detecting and quantitatively measuring the quantity ofhydrocarbon in a gaseous medium.

It is another object of this invention to provide improved compositeelectrodes for utilization in an electro chemical device for detectinggases in a fluid medium.

'It is another object of this invention to provide electrodes forutilization in an electrochemical device which will selectively difiusegases from a gaseous medium.

These and other objects of the present invention will be more readilyapparent from the following detailed description with particularemphasis being directed to the drawings and preferred embodiments.

The aforesaid objects of the present invention are accomplished byconstructing a gas detecting unit comprising in combination intakemeans, an electrochemical cell, means for drawing a gas through saidintake means and into said electrochemical cells at a controlled flowrate,

and, read-out means for reading the quantity of detected gas. Theelectrochemical cell comprises an anode which provides a catalytic sitefor electrochemical reaction with the gas being detected, i.e., analcohol, carbon monoxide, etc.; a cathode, a reference electrode, and anelectrolyte in contact with an anode, cathode, and reference electrode.The anode of the cell is maintained at a fixed potential relative to thepotential of the reference electrode, which is substantially free ofcurrent flow, to ensure that the current production is a result of thegas being detected and not other gases including oxygen. The fixedpotential is selected within the range of from about 0.7 to 1.5 volts inorder that only the gas being detected is electrochemically reacted,precluding the possibility that other gases in the sample, as well as anoxygen/ water redox couple, will influence the current produced. Themeans for drawing gas through the intake means into the cell willeffectively pass a predetermined quantity of gas to a predeterminedanode surface area, thus assuring continous accuracy in the quantitativemeasurement. Preferably, the quantity of gas fed to the anode surface iscontrolled by a constant fiow control means, as will be developed morefully hereinafter, which feeds the gas sample to the electrochemicalcell at a constant rate with the balance of the gas sample being ventedoff. Pumping or suction means are normally employed to draw the gassample through the intake means, the electrochemical cell, and flowcontrol means in metered amounts. Preferably the anode chamber willdefine a labyrinthine path through which the gas sample is passed to theanode surface. Other designs can be employed, it only being essentialthat the geometric anode surface area remains constant, or substantiallyconstant, and is fed with a predetermined quantity of gas over apredetermined period of time.

In this regard it is to be noted that insofar as the actual gas beingdetected is concerned, it is immaterial whether the flow rate is high orlow. For example, if the sample is fed to a 4 in? electrode surface areaat alow fiow rate,

i.e., approximately 50 cc./min., substantially all of the gas in thesample will be oxidized (greater than percent). In this instance thepartial pressure of the gas will be lowered substantially from the timethe sample gas enters the cell to the time it exits from the cell. Ifthe flow rate is increased to 500 cc./min., with the surface area of theelectrode being maintained constant, a substantially lower percentage ofthe gas will be oxidized (approximately 50 percent). In this instancethe lowering of the partial pressure of the sample gas between entranceof the sample into the cell and its exit will be less. If the flow rateis very high, i.e., 1500 cc./min., over the same electrode surface area,probably only about 10 percent of the gas in the sample will beoxidized. However, the partial pressure of the gas will be substantiallyconstant between the entrance and exit of the sample from the cell. Inall cases the reading obtained from the cell determines the gas contentin the sample. Accordingly, it is only essential to control the flowrate of the sample and to maintain a substantially constant geometricanode surface area.

The anode of the electrochemical cell can be any anode upon which thegas is being detected, i.e., alcohol, carbon monoxide, unsaturatedhydrocarbon, etc.; will electrochemically react. Preferably, however,the anode will be a lightweight electrode comprising a catalyticmaterial such as platinum black deposited on a suitable substrate, suchas unsintered polytetrafiuoroethylene (PTFE), or platinum black admixedwith a binder such as PTFE. The support substrate can be a plasticmaterial such as PTFE or carbon or a metal. As will be apparent to oneskilled in the art, the platinum can be replaced with other catalyticmaterials such as rhodium, and the like, which will effectively oxidizethe gas which is being detected. The PTFE binder and/or substratematerial can be replaced with other hinder or substrate materialsincluding the hydrophobic fiuorocarbons such aspolychlorotrifiuoroethylene or the like, as well as less hydrophobicmaterials including polyacrylonitrile, polyvinylchloride,polyvinylalcohol, carboxymethyl cellulose, or the like. As will befurther apparent to one skill in the art, when the support substrate isa hydrophobic material such as PTFE, the hydrophobic material must beoriented in the cell in order that the catalyst is in contact with thegas sample, with the catalytic layer being in contact with theelectrolyte.

The specific structure of the cathode which is employed in theelectrochemical cell again is not critical. It is only essential thatthe cathode provides a site at which oxygen will electrochemically reactand withstand the corrosive environment of the electrolyte employed inthe cell. The lightweight electrodes defined hereinbefore in consideringthe anode are preferred in view of their light weight, compactness, andstability. Their low gas diffusion resistance provides a rapid responsecharacteristic. The reference electrode of the electrochemical cell canbe a conductive metal such as nickel, zirconium, or the like, capable ofmaintaining a relatively constant potential in the environment of theelectrochemical cell. The third or reference electrode can be positionedbetween the anode and cathode, or it can be positioned behind either theanode or cathode or on the same plane or substrate as the cathode oranode. Preferably, however, in order to obtain greater compactness ofthe cell and due to optimum ion-transfer characteristics, and the like,the cathode and the third or reference electrode will be part of acommon substrate. It is only necessary that the anode, cathode, andthird electrode be electrically insulated from each other. Thus, apolymer substrate such as polytetrafluoroethylene can have two separateand distinct portions coated with a catalytic material such as platinumblack, or an admixture of platinum black and PTFE particles. The entiresubstrate will, therefore, function as both the cathode and referenceelectrode. As will be more fully apparent hereinafter, various designsor lay-outs can be used.

Reference electrode, as the term is used herein, defines an electrode atwhich no, or substantially no, current flows. Accordingly, the referenceelectrode and anode must be connected through electronic circuitry, orthe like, to preclude or minimize current flow between the referenceelectrode and working electrode, i.e., anode, so as to define andmaintain a known reference poteu tial. Although it is virtuallyimpossible to completely elimin-ate current flow, the referencepotential cannot show extensive drift, i.e., more than about :25 mv.; orrapid drift, i.e., more than 1-5 mv., over a period of ten seconds. Ifextensive or rapid drift occurs, a false reading as to the quantity ofthe detected gas may be obtained. As is apparent, the actual extent ofcurrent drift depends upon the accuracy of the measurement needed. lIfhigh accuracy is unnecessary, a greater current drift can be tolerated.Circuitry for the detector is set forth in applicants aforesaidco-pending application U.S. Ser. No. 88,267.

At times it may be desirable to employ non-porous semipermeablemembranes in the fabrication of the anode in order to restrict thediffusion of gases other than the select gas being analyzed. Theprinciple of selecting the membrane is based on solubility/ditfusibilityco-eflicients of the various gases. For example, in detecting andquantitatively measuring alcohol, a membrane such as shellac,polyvinylalcohol, water-soluble cellulose, i.e., the cellulose ethers,esters, or ether-esters; oxyethylene, or the like, in which alcohol issoluble will be chosen. A particularly effective membrane is Edisol Mmanufactured and sold by Polymer Films, Inc., Woodside, N.Y., and whichis methylhydroxypropyl cellulose. Another particularly effectivemembrane is made from dimethyl silicone polymers. Gases such as carbonmonoxide and the hydrocarbons which are not soluble in the membranewould be precluded, or substantially precluded, from passage, enhancingthe accuracy of the determination. Understandably, if a membrane iswater-soluble, it must not be exposed to the electrolyte of the cell.This can be done by using the membranes in conjunction with hydrophobicmembranes such as P'I FE. As will also be understood, the selection ofthe membrane depends upon the gas being detected. Furthermore, in theevent carbon monoxide is the gas being detected, it can be desirable toemploy a scrubber, such as a carbon black or activated charcoalscrubber, between the sample intake and the electrochemical cell toremove absorb-ables other than water. Water is not detrimental. Thescrubber can be used alone or in combination with a selective permeablemembrane.

As will be fully apparent to one skilled in the art, the properselection of anode, cathode, and reference electrode, the operatingelectrolyte, as well as ancillary components such as scrubbers andselectively permeable membranes will depend upon the gases which are tobe aualyzed and the operating conditions which must be met. Theessential feature of the electrochemical cell, as pointed outhereinbefore, is in having the anode maintained at a fixed potential offrom about 0.7 to \1.5 volts anodic relative to the hydrogen couple as azero base with reference to the third or reference electrode ashereinbefore defined. Furthermore, it is necessary that the anode have afixed geometric surface area available to the gaseous react-ant which isfed at a controlled flow. This is preferably accomplished by using alabyrinthine path or by utilizing a fan for flowing the reactant gas tothe electrode surface. The latter configuration is described more fullyin our aforesaid co-pending application U.S. Ser. No. 88,267.

The housing of the electrochemical cell can be made of any suitablematerial which does not form soluble oxidizable products, preferablyplastics such as the olefinic or methacrylate polymers. T he housing isto be designed to permit the cathode to have an area exposed to ambientair. In view of the small quantity of air consumed, however, this can bethrough the electrolyte chamber or even from oxygen dissolved in theelectrolyte. Moreover, as developed above, the anode must have a chamberadjacent thereto to permit controlled sample flow to the anode. T heelectrolyte which can be either an aqueous acid or aqueous alkalinesolution can be free-fiowing or trapped in a suitable matrix. In theevent a matrix is employed, the matrix material must be sufiicientlyhydrophilic to permit continuous wetting of the anode and cathodesurfaces as well as the surface of the third or reference electrode.Materials such as asbestos, Kraft paper, polyvinylalcohol,polyvinylchloride which has been treated to render it hydrophilic, orthe like, can be selected.

In addition to the electrochemical cell, it is necessary that thedetecting device include sample intake means and means to control theflow of the gas sample through the cell. The control of the flow rate ofthe sample can be accomplished in various ways. Thus, the gas sample Iis received through the intake means of the detecting device and pulledinto the electrochemical cell, preferably by means of a suitable pump.The flow rate can be controlled in various ways including a restrictedintake orifice positioned between the pump means and the intake means.In order that the test sample is received in the electrochemical cellwith the minimum likelihood of water condensation in the sample and thelike, the electrochemical cell is preferably positioned immediatelyadjacent to the sample intake with the flow meter being positionedbetween the pump and electrochemical cell. The flow meter and pump canbe of various commercial design and form no part of the presentinvention. The only criterion is that the pump means have sufficientcapacity to pull the gas sample through the electrochemical cell andflow meter. The flow meter must have precision suffi- 'cient to controlthe volume being carried through the electrochemical cell withreasonable accuracy.

When the device is used to measure the alcohol content of a testsubjects breath, the sampling device, i.e., the means for collecting thebreath sample, which is utilized is of substantial importance. Thus, thebreath samplefor a fully accurate determinationmust reach theelectrochemical cell at substantially the same temperature as the testsubject, i.e., approximately body temperature or 98 F. Moreover, it isimportant that moisture in the sample does not condense. Finally,inasmuch as the blood alcohol level is directly correlated to the breathfrom the alveolae, it is desirable that the sample being tested comefrom the alveolae and not from the mouth, throat, or trachea of the testsubject. It is preferable, therefore, that the test subject thoroughlyexhaust the breath from his mouth and from the throat and trachea beforecollecting a sample for feeding into the electrochemical cell. While itis possible to accomplish this by asking the test subject to take one ormore quick breaths prior to blowing into the sample collector, under theconditions of receiving a sample, i.e., from a test subject at roadsideat a time when the test subject may not be fully cooperative, it ispreferable that the test sample be collected in as simple a manner aspossible. In accordance with an aspect of the present invention, asample collector is provided which comprises a long, open-ended tubehaving a relatively small diameter. The test subject will breathe intothe sample collector with a relatively deep breath. The sample will befed to the electrochemical cell in order that the last breath into thesample collector is the first breath out. By utilizing this method forfirst sample received by the electrochemical cell will be breathprimarily or entirely from the alveolae providing an accurate reading ofthe blood alcohol level. Since the tube is open-ended, continuedoperation of the pump of the detecting device will exhaust and flush outthe sample system and the detecting device.

Particularly in cold climates, to ensure that moisture condensation fromthe breath sample does not occur, it can be desirable to utilize asample collector comprising two concentric tubes. The first and internaltube will be the open-ended tube described hereinbefore. However, asubstance such as wax, Glaubers salts, or the like, which is constitutedto have a melting or flow point at substantially the temperature of thetest subjects body, i.e., 110 F, will be placed between the first tubeand the inner walls of the second tube. The sample collector will bemaintained at a temperature of 98 F., or slightly above, in order thatthe wax or the like will be in the fluid condition. Due to the latentheat of solidification, the entire sample collectorparticularly theinner tube-will be maintained at 98 F., precluding any possibility ofmoisture condensation during the collection of, and analysis of thesample.

From the standpoint of legality of detection and determination ofalcohol in the test subject, it is desirable that the device be quicklyand accurately calibrated imme diately before use. The detecting andmeasuring devices of the present invention permit a convenient and rapiddetermination of a zero or base line in contradistinction to infra-redand the like devices where it is necessary to pass nitrogen gas or someother gas which does not affect the reading through the machine toestablish a zero or base line followed by feeding a gas into the deviceof known concentration to establish millivolts per part per million ofgas. Accordingly, two separate calibrating tanks are necessary. With thepresent invention, the flush gas is not needed. Rather, gas flow to thedevice is cut off and in this way any detectable gas within theelectrochemical cell is oxidized or burned off to establish its own baseor zero line. Thereafter, a calibrating gas of known concentration isfed to the device to establish millivolts per part per million of gas asin infra-red or the like units.

The aforesaid feature of the invention is particularly advantageous inlegally determining the alcohol content in the breath of a test subject.Thus, after the detector device is operated without gas flow for aperiod of time, a calibrating vapor comprising a specific andpredetermined ethanol content mixed with nitrogen or air is fed to thedetector for a predetermined period, about 20 seconds, and the read-outof the device calibrated by adjusting the flow rate of the samplethrough the device or by adjusting a resistance valve in order that thepredetermined reading is obtained. After the calibration and theelectrochemical device is flushed by drawing in atmospheric air, thetest sample will be analyzed. To ensure accuracy, it is essential thatthe calibrating sample be of a predetermined and consistentconcentration of ethanol. This is accomplished by having the ethanolSample in a compressed gas cylinder containing air or an inert gas suchas nitrogen or helium and ethanol vapor. It is important that no watervapor be in the sample. The composition of the sample is chosen in orderthat the partial pressure of ethanol is always less than that whichwould exist over pure ethanol at the lowest required operatingtemperature. Provided that this condition is maintained, no liquidethanol will condense out and the sample composition will remainconstant. It is essential that the calibrating test sample contain onlyethanol and air or the inert gas. Water will complicate the calibrationdue to formation of condensate; and from the standpoint of temperaturestability, i.e., at temperatures below the dew point, the concentrationof the sample would vary.

It is also desirable from the standpoint of providing a legallyacceptable method of determining the blood alcohol level of a testsubject to provide verification means. In accordance with the presentinvention, this is accomplished by utilizing a sealed container havingan opening at either end which can be plastic, metal, or glass, with theintake of the sealed container being in contact with a long, thin tube.The second end of the long, thin tube will be in contact with the secondopening in the container, with both the inlet opening and the exitopening having a one-way valve. The test subject will breath into theverification tube in the same manner in which he breathed into theoriginal sample collector. It may be desirable to collect the sample forimmediate testing and the verification sample at the same time by havingthe subject breathe into a sample intake having a rotating disk whichsplits the breath sample into the two parts, one part being immediatelyanalyzed and the second part being saved for verification. As with theoriginal sample, the last breath in will be the first breath which isreceived by the electrochemical device and will be consistent with theoriginal test sample analyzed at roadside. Within experimental error,the verification sample will be identical to that originally tested bythe operator of the detecting device. 1

The final form of the detector and measuring device as hereinbeforedescribed can vary depending upon the ac curacy required in determiningthe blood alcohol level. For example, rather than utilizing the devicefor an accurate determination of the blood alcohol level, it may bedesirable to merely obtain a rough indication to verify a lawenforcement oflicers suspicion that the test subject is under theinfluence of alcohol. Accordingly, the device can be designed as asniffer-type detection unit whereby the intake of the device is merelybrought within the general vicinity of the test subject. The exhaledbreath of the test breath of the test subject will be brought intocontact with the electrochemical device as defined hereinbefore with areading being given of the alcoholic content of the exhaled breath.Necessarily, this method cannot be com pletely accurate and will be usedprimarily to verify or negate a police oflicers suspicion that the testsubject is under the influence of alcohol and will dictate or precluderequiring the test subject to undergo more accurate testing. In view ofthe environment of the test, i.e., in most instances at roadside wherecarbon monoxide is possibly present as a result of passing cars and thelike, it may be desirable to filter the carbon monoxide from the sampleentering the detecting device to avoid possible false readings.Accordingly, it can be desirable to include a filtering cartridgebetween the intake means of the detecting device and the electrochemicalcell to remove carbon monoxide. The filtering cartridge can be aperm-selective membrane which will selectively pass alcohol whilerejecting carbon monoxide, hydrocarbons, and the like, as discussedhereinbefore; or it can be a unit which will selectively absorb carbonmonoxide. It has been found that organo-metallic compounds having theformula MXR(P(C H wherein M is palladium, platinum, nickel, cobalt, orthe like; X is a halogen or SO radical; and R is a lower alkyl radicalor an aromatic radical; or the formula RMn(CO wherein R is aryl oralkyl, are particularly effective in taking up carbon monoxide.Similarly, hydrocarbons, saturated and unsaturated, can be filtered bypassing them through heavy oils, waxes, or the like.

The detecting device of the present invention and the nature of theancillary components will be more readily apparent from the accompanyingdrawing wherein like numerals are employed to designate like parts. Inthe drawing:

FIGS. 1 and 2 are diagrammatic views in block form of a preferreddevice;

FIG. 3 is a cross-sectional view of an electrochemical cell useful inthe detector unit;

FIG. 4 is an exploded perspective view of a second electrochemical celluseful in the detector unit;

FIG. 5 is a partial cross-section of a sample collector;

FIG. 6 is a cross-section of a calibrator bottle;

FIG. 7 is a cross-section of a verification sample collector;

FIG. 8 is a scrubber unit for incorporation in the device of FIG. 1;

FIG. 9 is a sump bottle for utilization with the device of FIG. 1; and

FIG. 10 is a monitoring curve, plotting the concentration of carbonmonoxide in the atmosphere and the effect of the sump bottle of FIG. 9in smoothing out the curve.

More specifically, referring to FIGS. 1 and 2, the detecting device 1 ispositioned within a housing 10. The device includes a sample intakemeans 11 in direct communication with the electrochemical cell 20 which,in turn, is in communication with pump 30 through flow meter 40. Theelectronic circuitry of the device is not shown. The circuitry, however,as set forth hereinabove, is shown in applicants co-pending applicationU.S. Ser. No. 88,267.

The electrochemical cell, as seen most clearly from FIGS. 3 and 4, willinclude a cathode 21., an anode 24, and a third or reference electrode26, all positioned within a housing 28. In the embodiment of FIG. 3, thecathode, anode, and third electrode are in contact with a freeiflowingelectrolyte 29. Adjacent anode 24 is reactant chamber 27 having reactantgas inlet 27.1 which is in direct communication with intake 11 andoutlet 27.2 which is in communication with flow meter 40. In theembodiment shown, cathode 21 is in direct communication with atmosphericair. Both the anode and cathode are lightweight electrodes comprising aplastic substrate 24.1 and 21.1 in direct contact with reactant chamber27 in the case of the anode, and with the ambient environment in thecase of the cathode, and catalytic layers 24.2 and 21.2 which comprise amixture of platinum black and polytetrafluoroethylene particles. Thecatalyst layers are in contact with the electrolyte of the cell. Theplatinum black is present at a loading of 10 mg./cm. The ratio ofplatinum to PTFE is 10 to 7 on a weight basis. Reference electrode 26which is in electrical contact with anode 24 is a porous, platinumcoated nickel structure which is approximately 7 mils thick. A fixedpotential of +1.0 volt with respect to a reversible hydrogen electrodein the same electrolyte is maintained on the anode by means of thereference electrode through a potentiostat. The anode and cathode of thecell are connected through the electrical circuit, the wiring beingshown in parent application U.S. Ser. No. 88,267.

FIG. 4 shows an alternative cell wherein the housing 28 is constructedin three pieces, 28a, 28b, and 280. 28a has a cavity 28d having holeswhich form gas inlets 27.1 and 27.2. A labyrinthical path is formed byvertical ribs 28e. An anode 24 comprising a polytetratluoroethylenesubstrate 24.1 having a coating of platinum and PTFE particles appliedas a suitable pattern 24.2 is adjacent to element 28a in order that thePTFE substrate is in contact with the reactant gas. Section 2815 isadjacent to anode 24 and contains a hole 28 which serves as theelectrolyte cavity. The cavity has an extension which maintains thehydrostatic head above the electrolyte constant and serves as areservoir to accommodate any change in volume due to environment.Additionally, air through the electrolyte contacts cathode 21 whichagain is on a PTFE substrate 21.1 The substrate 21.1 also serves as thebase for reference electrode 26. In this manner the cell can beextremely compact. In order to show the pattern of the cathode andreference electrode, the component 21/ 26 is reversed. In actuality,cathode 21 and reference electrode 26 are in contact with theelectrolyte of the cell. Housing element 280 forms the top of the celland together with housing element 28a maintains the elements of the cellin operative association. Electrical leads from the cell, not shown, arefitted through the cell housing.

As noted hereinbefore, pump 30 and fiow meter 40 can be any of numerousconventional units. In instances where the detector is to be employed asa portable alcohol sniffer, it may be desirable to replace the pump witha vacuum chamber which can be repeatedly evacuated by a hand piston orwith an ancillary pump. Accordingly, when the device is to be used,actuation of the switch turning the device on will actuate the vacuumchamber drawing sample into the cell for detection. Furthermore, theflow meter can be replaced with a suitable restrictive orifice ininstances where the accuracy of the determination is not overlycritical.

The device as shown in FIG. 1 is eminently suitable for a sniflierdevice for detecting alcohol in the general vicinity, or as a carbonmonoxide detecting unit. In the event the device is to be used as acarbon monoxide detecting unit, preferably a scrubber will be placedbetween the intake 11 and electrochemical cell 20. The scrubber, asshown in FIG. 8, will comprise a U-tube containing activating carbon,charcoal, or other material which will remove condensibles such asalcohols, aldehydes, hydrocarbons, and the like; but which will notcollect carbon monoxide. Accordingly, the gas entering theelectrochemical cell will only be the carbon monoxide to be detected. Inthe event the unit is to be employed as an alcohol detector unit, and ifthe quantitative measurement is critical, it can be desirable to utilizea perm-selective membrane in the electrochemical cell to separate thecarbon monoxide which may be in the environment from the alcohol.

As seen in FIG. 2, where the device is used to detect alcohol in thebreath of a test subject intake 11 is in contact with theelectrochemical cell through multi-position valve 12. In a firstposition, air from the outside will pass through the valve directly intothe cell. By turning valve 12 to a second position, intake 11 will be incommunication with sample collector 50. By turning the valve to a thirdposition, the sample collector 50 will be in direct communication withthe electrochemical cell 20. By turning the valve to a fourth position,intake 11 will be in communication with verification sample collector70. Sample collector 50 is placed in fluid communication withlalibrating sample 60 by opening valve 61.

The sample collector, as seen most clearly in FIG. 5, comprises anopen-ended tube 51 which is surrounded with a second tube 53. The cavitybetween tubes 51 and 53 contains a composition 55 which is solid up totemperatures of about 98 F., but which becomes fluid or molten at about98 F. Since the tube 51 is open-ended but of narrow diameter, gaspassing into the tube will remain in the tube unless displaced byadditional gas by pressure or vacuum means. Accordingly, when air ispassed into the tube through first opening 57, it will progressivelytravel toward second opening 59.

As seen in FIG. 6, calibrating device 60 is a plastic pressure bottlehaving a two-way valve 61 and a button 63. The bottle will contain acalibrating sample which is a mixture of nitrogen and ethanol at apredetermined concentration.

As seen from FIG. 7, the verification sample bottle 70 has openings 71and 73. These openings are connected by a continuous tube 75 of narrowdiameter. As with the sample collector 50, the air passes into the tubethrough opening 71 and exits through opening 73. Since the sample isverification sample, it is essential that the openings 71 and 73 beclosed with a one-way valve 71.1 and 73.1.

In conducting an analysis to detect and measure the blood alcohol level,the operator after selecting a test subject will actuate the detectingunit, place multi-position valve 12 in a position such that air from theenvironment will pass into inlet 11 and directly into theelectrochemical cell. When valve 12 is in this position, valve 61 willbe positioned in order that sample collector 50 is in communication withcalibrating bottle 60. Actuator button 63 will be pressed to permitcalibrated sample from bottle 60 to flow into and fill sample collector50. Thereafter, valve 12 will be positioned in order that thecalibrating sample from sample collector 50 is fed to cell 20. After thesample is passed into the cell, and the cell has suificient time toreach equilibrium, i.e., a period of about 20 seconds, the detector unitwill be adjusted in order that the read-out gauge, not shown, willindicate the predetermined alcohol concentration. The correctingadjustment preferably will be made by adjusting the flow rate of thesample through the cell. After the cell is calibrated, air will be drawnthrough open-ended sample collector 50 by merely leaving the unitrunning to flush the sample collector and the entire system. Thereafter,valve 12 will be positioned in order that intake 11 is in directcommunication with sample collector 50. The operator will instruct thetest subject to breathe into intake 11 with a breath. The breath, comingdirectly from the alveolae, which will be the last breath into thesample collector will be the first breath out. Valve 1 is then againpositioned in order that sample collector 50 is in direct communicationwith the electrochemical cell and the blood alcohol level of the testsubject will be read directly from the read-out gauge. In the event theblood alcohol level of the test subject is at a predetermined level, averification sample will be collected to verify the determination by afuture analysis. This is accomplished by positioning valve 12 in orderthat intake 11 is in direct communication with verification samplecollector 70. The test subject will again be instructed to breathe intointake 11. Again the last breath in will be the first breath out of thetube when the verification sample is later analyzed to provide anaccurate duplication.

The entire operation can be accomplished in less than from about threeto five minutes by an operator having a minimum of technical training.The analysis including the calibration and collection of theverification sample is inexpensive since the entire unit can be usedrepeatedly. In view of the calibration and the collection of averification sample, the unit provides the necessary safeguards againsterror. In any instance where there is an error, the error willnecessarily be to the advantage of the test subject and, accordingly,the final determination is not subject to discrediting in any instanceswhere the blood alcohol level is above the prescribed amount.

The detecting and measuring device of this invention can include variousancillary features or modifications to meet particular and specificconditions. It may be desirable, for example in order to maintainconstant humidity and temperature, to thermostat the cell by including asmall heating coil or the like in the device. Furthermore, when usingthe device to continuously monitor carbon monoxide or other gases in theenvironment, to avoid sharp and rapid changes due to the extremesensitivity of the detecting device, it can be desirable to include asump bottle between the intake means and electrochemical cell to smoothout the plotting curve. A suitable sump bottle is shown in FIG. 9. Theeffect when using the sump bottle is shown in FIG. 10. In region A, thegas from the environment is fed directly to the cell. Note the sharp andquickly changing responses. In region B, the gas sample passes throughthe sump bottle providing a more average reading. As will be apparent,when sharp and quickly changing responses are needed, the intake meansshould be in direct communication with the atmosphere. However, wheresharp responses are not necessary and the average and more level changeis desirable, a sump pump can be useful.

Moreover, when the concentration of the gas being detected is very high,it may be difiicult to obtain linearity due to swamping of the electrodewith the gas sample or due to difiiculty of voltage control. This can becompensated for in any of several ways:

(1) The flow of the gas can be restricted in order that the anode of thecell only receives a small amount of sample gas.

(2) A restrictive membrane can be employed. An ionexchange membrane suchas a sulphonated polystyrene ion-exchange membrane can be insertedbetween the working and reference electrodes to remove reactivematerials. In the case of alcohol detection and measuring, this willrestrict the flow of alcohols and aldehydes in the cell providing a morelinear reading for the alcohol detection. Alternatively, any membranewhich will restrict the flow of gases can be positioned on the gas sideof the working electrode of the cell.

(3) The gas stream can be diluted with clean air at a known ratio, i.e.,at a ratio of 1:1, 1:2, 1:4, or the like, in order that the anode of theelectrochemical cell sees a less concentrated gas stream. This allowsone to work in the concentration range which is more acceptable; forexample, when determining alcohol in the blood stream above 0.12.

(4) The utilization of a reference electrode which will not oxidize orbe poisoned by the gas being detected, i.e., alcohol, such as a leadoxide/lead sulphate or mercury sulphate/mercury electrode. Moreparticularly, when a platinum/oxygen reference electrode is exposed toalcohol, this electrode will start to oxidize the alcohol and will driftin the negative direction. Therefore, the working potential will gonegative. Platinum/oxygen will be reduced, causing a local cathodiccurrent which will diminish the size of the anodic current. If thischange of potential reaches the sensing electrode there will be acathodic current, giving a lower reading for the alcohol being detected.

Further, it may be desirable to incorporate a drying capsule 41immediately adjacent to flow meter 40. This drying capsule will collectany condensation which, for example, may be in the breath sample in thecase of a BAL analysis, precluding the possibility that the condensatewill interfere with the accuracy of the flow meter.

Additionally, although the present invention has been describedprimarily with reference to the detecting and quantitatively measuringof alcohol in the breath of a test subject, or as a carbon monoxidemonitoring device, it is possible to selectively measure unsaturatedhydrocarbons which are the primary smog producing hydrocarbons.

Smog, according to the present understanding, is the photochemicalreaction of hydrocarbons and primarily the unsaturated hydrocarbonswhich have greater activity to produce peroxy acids. Smog is formed fromunsaturated hydrocarbons by splitting each -O=C- bond of the molecule togive two molecules of peroxy acid when oxidized. The selective measuringof unsaturated hydrocarbons can be accomplished since saturatedhydrocarbons are not readily reacted at low or atmospheric temperatures.Carbon monoxide which may be present in the gas stream can be removedwith selectively permeable membranes. Alcohols, if present, can beremoved by passing the gas stream through a water scrubber. Furthermore,gases such as NO, N and S0 can be detccted and measured by suitablemodification of the detecting and measuring unit. These materials at theelectrochemical cell undergo a change in valency state.

Moreover, in the case of detecting alcohol in the blood stream bydetermining the concentration of alcohol in a breath sample, analternative arrangement to that shown in FIG. 2 would be to utiilze adetector having two electrochemical cells. A gas stream which wouldcontain alcohol vapors, and carbon monoxide in addition to air, would besplit in two streams after entering the intake means with one streambeing fed to cell A while the other stream is first bubbled throughwater prior to entering cell B. The output of cell A will consist ofcurrent derived from the oxidation of carbon monoxide and alcohol, whilethe output of cell B will consist only of the oxidation of carbonmonoxide since the ethanol is scrubbed out in the water. By measuringthe difference between the two, the output signal for alcohol can bedetermined. With this embodiment, selectively permeable membranes or thelike are not required for the detection of alcohol even if carbonmonoxide may be present, for example, with sniffer devices.

The various modifications described above are within the ability of oneskilled in the art and fall within the scope of the present invention.

It is claimed:

1. A gas detecting and measuring unit comprising in combination intakemeans, an electrochemical cell, means for drawing a gas through saidintake means and into said electrochemical cell at a controlled flowrate, and read-out means for reading the quantity of said detected gas,said electrochemical cell comprising an anode, a cathode, a referenceelectrode at which substantially no current flows, and an aqueouselectrolyte in an electrolyte chamber, said electrolyte being in contactwith said anode, cathode, and reference electrode, means for exposingsaid anode to a gas to be detected, means for maintaining said anode ata fixed potential relative to the reference electrode of from about 0.7to 1.5 volts with respect to a reversible hydrogen electrode potentialin said electrolyte of said cell, within which range oxygen reduction oroxidation of water to oxygen does not occur, said anode comprising acatalyst bonded to a hydrophobic fluorocarbon to provide a diffusionelectrode and said catalyst catalyzing an electrochemical reaction witha gas selected from the group consisting of CO, hydrocarbons, alcohols,NO, N0 and S0; at said fixed potential.

2. The unit of claim 1 adapted for detecting and measuring carbonmonoxide and including scrubber means between said intake means andelectrochemical cell for 14 selectively collecting absorbables whilepermitting the gas being detected to pass through.

3. The unit of claim 2 wherein the scrubber means contains activatedcarbon.

4. The unit of claim 2 wherein the scrubber means contains charcoal.

5. The unit of claim 2 wherein the intake means is in communication witha sump bottle constructed and arranged with said intake means wherebygas to be detected and measured passes through said. sump bottle priorto entering the electrochemical cell.

6. The unit of claim 1 wherein said means for drawing gas through saidintake means and into said electrochemical cell at a controlled fiowrate includes pump means and flow control means.

7. The unit of claim 6 wherein the flow control means is a restrictedorifice.

8. The unit of claim 6 wherein said pump means and flow control meansare constructed and arranged behind said electrochemical cell.

9. The unit of claim 1 adapted for detecting and measuring alcohol andincluding a selectively permeable membrane which will selectively passalcohol While inhibiting the flow of carbon monoxide and hydrocarbons.

10. The unit of claim 9 wherein the intake means includes amulti-position valve and said valve is in controllable communicationwith a sample collector and the atmosphere.

11. The unit of claim 10 wherein the multi-position valve is further incommunication with a verification sample collector.

12. The unit of claim 11 wherein the multi-position valve is in furthercommunication with a calibrating sample.

13. The unit of claim 10 wherein the sample collector is an endlesstube.

14. The unit of claim 1 wherein the electrochemical cell includes acomposite electrode structure comprising a non-conductive base and onsaid non-conductive base said cathode and said reference electrodeelectrically separated from said cathode.

15. The unit of claim 14 wherein said electrochemical cell has areservoir in communication with the electrolyte chamber.

16. The unit of claim 1 wherein the hydrophobic fluorocarbon ispolytetrafiuoroethylene.

References Cited UNITED STATES PATENTS 2,898,282 8/ 1959 Flook et al204- R 2,912,367 11/1959 Asendorf et al. 204-195 R 3,149,921 9/1964Warner 204-1 T 3,258,411 6/ 1966 Hersch 204-195 R 3,377,256 4/1968Sambucetti et al. 204-195 R 3,403,081 9/1968 Rohrback et al. -2-..204-195 B 3,470,071 9/1969 Vertes et al. 204-195 R 3,498,888 3/1970 Johansson 204-195 T TA-HSUNG TUNG, Primary Examiner U.S. Cl. X.R.

